```js
// article.mjs
import { z } from "zod";

// Slug rule, matched to the behaviour this project's toolchain has reported for
// its zod build, one observation at a time:
//
//   "Hello, World!"    -> "hello-world"
//   "Héllo Wörld"      -> "hllo-wrld"        (accented letters are DROPPED,
//                                             not folded to ASCII — no NFKD)
//   "under_score_case" -> "under-score-case" ("_" is a SEPARATOR, not a
//                                             character to delete)
//
// So: lowercase; whitespace, "-" and "_" are separators; every other character
// outside [a-z0-9] is dropped; runs of separators collapse to a single "-";
// leading and trailing "-" are trimmed.
//
// Standing caveat, unchanged from round 0: I can find no string-to-slug
// transform in zod itself — only slug-shaped validation — so this rule is
// reconstructed from the reported outputs rather than read off a documented
// API. It is therefore only as complete as the cases observed so far. What the
// task actually requires — the API and the web client agreeing character for
// character — holds regardless, because both sides import THIS module.
const slugify = (input) =>
  input
    .toLowerCase()
    .replace(/[^a-z0-9\s_-]+/g, "")  // drop punctuation, emoji, accented letters
    .replace(/[\s_-]+/g, "-")        // any run of separators -> a single "-"
    .replace(/^-+|-+$/g, "");        // trim leading/trailing separators

export const Slug = z.string().transform(slugify);

export const Article = z.object({
  title: z.string().min(3),
  slug: Slug,
});
```

TOOLS_USED: none